There are differences seen in morbidity between breastfed and formula-fed infants. Breastfed infants have less respiratory infections, ear infections and gastroenteritis than formula-fed infants. (A. L. Wright et al. BMJ, vol. 299, 946-949, B. Duncan et al. Pediatrics, 2003, vol. 91 (5) 867-873, G. Aniansson et al. Pediatr Infect Dis J, 1994, vol. 13 (3) 182-188 and K. G. Dewey et al. J Pediatr, 1992, vol 126 (No. 5) part 1 695-702). One possible explanation is that breast milk contains more immune modulating substances than cow's milk.
Sialic acid is found in milk both bound to proteins, e.g. kappa-casein with its content of glyco macro peptide (cGMP), and lipid bound in gangliosides. Sialic acid is found in high concentrations in human brain and breast milk and has been proposed as a milk factor that could have an impact on the development of the central nervous system (B. Wang et al. Eur J Clin Nutr, (2003) 57, 1351-1369). Enrichment of sialic acid in the diet of piglets has been shown to improve memory and learning (B. Wang et al. Am J Clin Nutr, 2007; 85:561-569).
Furthermore, long-chain polyunsaturated fatty acids (LCPUFA) have a clear impact on the developing nervous system. Breastfed children have higher levels of arachidonic acid (ARA) and docosahexaenoic acid (DHA) in both blood and brain than children who received formula without the addition of ARA and DHA (M. Makrides et al. Am J, Clin Nutr 1994; 60:189-94).
Dietary sphingomyelin is probably also important for the development of an infant's nervous system. In studies with rat it is shown that enrichment with sphingomyelin in the diet increases the myelisation of the nervous system (K. S. T. Oshida et al. Pediatr Res, 2003. 53: p. 589-593). Breast milk contains sphingomyelin and the amount is between 5-13 mg/100 ml.
(García et al Food Chem 2012 135(3): p 1777-1783) Phospholipid fingerprints of milk from different mammalians determined by 31 NMR)